“Additive manufacturing” is a broad term that generally describes a manufacturing process whereby a three-dimensional model of an object to be fabricated is provided to an apparatus (e.g. a “three-dimensional printer” or a “3-D printer”), which then autonomously fabricates the three-dimensional object by depositing, or otherwise forming, constituent material in the shape of the object to be fabricated until it is fully formed.
There are various additive manufacturing techniques. One exemplary additive manufacturing technique is fused deposition modeling. Such a technique involves use of a fused filament fabrication printer, which is an extrusion-based printer, and is often commonly referred to as a 3-D printer. Such printers generally use a printhead that applies layers of thermoplastic, a metal or metal-containing carrier, or polymers and composites that are doped with a variety of secondary materials such as wood and carbon fiber to create models, prototypes, patterns, and production parts. Such fused filament fabrication works on an “additive” principle by laying down material in layers. This technique was described in U.S. Pat. No. 5,121,329, the entire disclosure of which is hereby incorporated herein by reference.
Exemplary fused filament fabrication printing involves a plastic filament (or metal wire) that is unwound from a coil and supplies material to an extrusion nozzle that can start and stop material flow. The nozzle is heated to melt the material and can be moved in both horizontal and vertical directions by a numerically controlled mechanism which is often directly controlled by a computer-aided manufacturing (CAM) software package. The model or part is produced by extruding small amounts of thermoplastic or other material to form layers as the material hardens immediately after extrusion from the nozzle.
Such 3-D printers typically rely upon a wirefeed system. In a wirefeed system, the filament or wire (hereinafter collectively referred to as “filament”) is pushed by a drive motor into a heated nozzle within the print head. The heated nozzle melts the filament material before it is forced through a small diameter die of the print head. The heating of the nozzle is carefully controlled to manage the heating process so that a still-solid upstream portion of the filament material acts like a piston or plunger in a syringe to drive a melted downstream portion of the filament material out of the nozzle before itself melting, in a continuous-feed process. The wirefeed system is thus limited to materials that are sufficiently rigid to be pushed through the nozzle by the drive motor, and to act as a piston/plunger. By way of example, sufficiently rigid plastic materials such as ABS, HDPE, PLA, and PVA are typically suitable for use in such wirefeed systems.
Though such relatively-rigid materials are suitable in many applications, it has been found to be desirable in some applications to manufacture objects of materials that are less-rigid than materials that are sufficiently rigid for use in such wirefeed extrusion systems. By way of example, it may be desirable to use less-rigid materials such as thermoplastic elastomers for the manufacture of objects for use in soft robotics, medical and mold-making applications. Further, while less-rigid plastics or other materials cannot exert enough force on molten plastic below them to extrude in a wirefeed extrusion system, excessively brittle materials may also be unsuitable for such wirefeed extrusion systems. Excessively brittle materials are prone to snap, rather than compress effectively, as threaded through a wirefeed extrusion system.
In laboratory, bench top and industrial applications, large-scale screw-drive extrusion apparatuses are used. Such screw-drive extrusion apparatuses are significantly larger than is feasible for most 3-D printing applications, such apparatuses typically being large in scale (often measured in feet or yards) and sufficiently heavy (often measured in hundreds or thousands of pounds) to be suitable for rapid movement about a print bed of a 3-D printer to build a 3-D printed object. Further, such screw-drive extrusion apparatuses are typically designed to operate according to a single set of operative conditions. For example, they are often tuned to work at a specific temperature, with a specific feed rate, and with a specific extrudate material. This is not useful for a 3-D printer which, ideally, can be used with any plastic the user desires, and at various speeds.
Further, a common form of 3-D printing uses plastics as the extrudate. Unfortunately, plastics don't behave ideally with respect to a screw-drive extrusion process in that the liquid plastic tends to become more fluid as the screw is driven faster to feed move liquid plastic. This means that higher print speeds often require non-proportional increases in extruder speed. Additionally, the energy required to melt the feed material would vary with the extrusion flow rate/feed rate.
Improvements of fused filament fabrication printers requires an increase in printing speed, printing with multiple materials, and lower printer costs.